1. Field of the Invention
This invention relates to a method of enhancing oil recovery from a subterranean hydrocarbon reservoir and to compositions for use in such methods.
2. Background
Hydrocarbons, i.e. gas and oils, are a limited resource and thus it is important to maximize the amount of oil that is recovered from underground reservoirs.
For certain reservoirs, particularly heavy oil reservoirs in which the oil contains large quantities of long chain hydrocarbons, paraffins, waxes, aromatics (including polyaromatic hydrocarbons—PAH), terpenoids, asphaltenes, etc., oil sand or shale reservoirs, and bitumen reservoirs the techniques currently used result in the recovery of less than 10% wt. of the oil in the reservoir. To a large extent this is because the oil is of such a high viscosity, or otherwise flows so poorly, that only limited quantities will reach the production wells.
One approach that has been adopted to this problem is to inject superheated steam down injection wells above the production wells, e.g. in substantially horizontal sections of the bore holes where the injection bore hole is above the production bore hole. The temperature increase resulting from superheated steam injection serves to reduce the viscosity of the heavy oil which then, under the influence of gravity, flows more readily into the production bore hole. This procedure has been referred to as steam-assisted gravity drainage (SAG-D) or VAPEX.
A further approach to increasing hydrocarbon recovery is hot solvent extraction in which a heated organic solvent is injected into the matrix to reduce the viscosity of the hydrocarbon and improve its flow characteristics in the matrix. In this technique, injection may be into an injection bore hole (i.e. as with steam injection) or it may be into the production bore hole. Typically the hot solvent used is selected from naphtha, diesel, toluene, and other hydrocarbon fractions. The injection temperature will typically be in the range 20 to 400° C., especially 80 to 100° C.
Yet another extraction enhancement procedure is cold heavy oil production with sand (CHOPS) which involves sand influx into the production well. Another procedure is hydraulic fragmentation (fracking) of the matrix at the production well. Further examples of enhanced oil recovery techniques for heavy oil, oil sand or bitumen reservoirs include cyclic steam stimulation (CSS), and pulsed pressure flow enhancement. Down-hole generation of gases to increase down-hole pressure and hence oil flow into the production well may also involve direct contact steam generation and thermal oxidation processes (to generate CO2 from combustion of hydrocarbons down-hole).
The techniques however are cumbersome, environmentally unfriendly and improvements and alternatives are desirable.